Various efforts have been made to improve the fuel efficiency and emissions of vehicles. For example, an auxiliary power unit (APU) may be included in a vehicle. The APU may be activated to maintain engine coolant temperature during a non-moving condition of the vehicle. By keeping the coolant at a desired temperature via the APU, the primary engine of the vehicle may be shut down during the non-moving operation to conserve fuel. Further efforts to increase fuel efficiency and/or reduce emissions have included down-sizing of the vehicle. However, standard APUs may comprise a large amount of packaging space in the vehicle, and such down-sized vehicles may not be able to accommodate an APU.